Arthritis is one of the most prevalent causes of adult impairment with the small joints of the hand and wrist commonly affected. Disability results from the pain produced by the grinding together of adjacent bones whose natural articular surfaces once covered with slippery cartilage have become rough from disease. Interposition arthroplasty is a common procedure where a biologic or synthetic material is interposed between the bones once the degenerated joint surfaces are removed. The interpositional material serves as a cushion to prevent bone to bone contact and to prevent the collapse of the adjacent bones into the surgically created void. One form of the disease, osteoarthritic degeneration of the thumb basal joint (which is also known as the trapeziometacarpal or carpometacarpal (CMC) joint) is particularly prevalent and debilitating, affecting as many as half of all post-menopausal women. The CMC joint is where the saddle-shaped trapezium bone articulates with the first metacarpal bone allowing motion like that of a mechanical universal joint. An arthritic CMC joint becomes painful enough to limit everyday activity such as grasping or pinching. Symptoms can often be treated with physical therapy, rest, splinting or anti-inflammatory medication. If pain persists surgery may be indicated to allow return to activities of normal daily living. Interposition arthroplasty, the most commonly performed surgical procedure for treating CMC arthritis, has been in use since the early 1970's.
Surgical intervention for treatment of CMC arthritis begins with removal of the diseased tissue, usually the entire trapezium bone or a portion thereof. To prevent the collapse of the first metacarpal bone into the space thus created, a wire pin is often used to align the base of the first metacarpal bone with the base of the index metacarpal. The pin serves as a temporary stabilizer. A tendon, such as the palmaris longus or flexor carpi radialis is harvested from the forearm and rolled up, resembling a rolled "anchovy" or jelly-roll. The anchovy is then sutured to prevent unrolling and is interposed between the base of the thumb metacarpal and the scaphoid, the space previously occupied by the trapezium bone. In some cases a suspensionplasty is performed wherein a further piece of tendon is used to tie the base of the thumb metacarpal to the base of the index metacarpal, thereby "suspending" the thumb metacarpal. The wire pin is left in place for about 4 to 6 weeks while healing occurs. It is usually 8 weeks or more before patients are allowed unrestricted activity.
Although the results of tendon interposition are acceptable, there are a number of drawbacks to this procedure. As with any procedure requiring taking a graft, there is additional surgical trauma and morbidity associated with the graft donor site. In many circumstances, there is not enough tendon available from which a graft may be harvested or the quality of the tissue is inadequate. Another major drawback is the amount of time it takes to harvest a tendon graft and prepare it for interpositional placement. Adding a suspensionplasty can also significantly increase operating time. There is evidence that during healing, the tendon grafts weaken and lose structural strength, necessitating the use of pins to help hold the thumb metacarpal in the right position while dense scar forms which will ultimately support the metacarpal.
Prosthetic material has also been used to treat CMC arthritis. One of the most widely used materials has been silicone rubber. Several implant designs have been manufactured from these materials such as the Swanson design (Wright Medical Technology, Inc., Arlington, Tenn.) which was a cylindrical spacer with a long stem fitted into a canal reamed into the metacarpal. Another design of silicone rubber implant was the Ashworth-Blatt Design (Wright Medical Technology Inc., Arlington, Tenn.) which was a button-shaped spacer with a small locating pin. Problems with fracture and dislocation of these implants led to the Stubstad design (U.S. Pat. No. 3,745,590) which incorporated a polyethylene terephthalate or polytetrafluoroethylene fabric mesh for improved strength and to allow tissue ingrowth for fixation to the metacarpal. The Eaton design (U.S. Pat. No. 3,924,276) addressed dislocation with a perforation to allow fixation by attaching a slip of the flexor carpi radialis tendon. All of these silicone rubber devices were subject to dislocation, fracture, abrasion and fatigue which led to the generation of small particles of silicone. The term "silicone synovitis" was coined to describe the chronic inflammatory reaction that resulted from this liberation of silicone particles.
Other implant materials such as titanium were used that would not be susceptible to abrasion and fatigue. These hard implants have failed due to their inability to conform to the intricate contours of the adjacent bones, causing damage to the bones over time.
Many inventors attempted to address the problems associated with hard implants and degradation of silicone implants by designing two piece implants that were intended to reconstruct an articulating joint. Many of the early designs were basically a ball and socket joint on simple stems. More recently Carignan et al (U.S. Pat. No. 4,955,916) disclose a two piece implant featuring a mesh disk for bone ingrowth into the carpal component. Bouchon et al., (U.S. Pat. No. 5,507,822) disclose a two piece design featuring a threaded metacarpal stem that is screwed into position. Hollister et al (U.S. Pat. No. 5,549,690) features a mathematically modeled torus shaped articulating surface that more closely resembles the natural articulating surface. A device with saddle-shaped articulating surfaces allowing rotary circumduction is disclosed by Linscheid et al., (U.S. Pat. 5,405,400). These types of devices have historically met with numerous problems such as loosening, dislocation, difficult implantation technique, and high cost. Additionally, these devices, as with the silicone devices, require a complete range of sizes to allow for patient to patient variability in size and anatomy. More recently, there have been attempts to find alternative materials for interposition arthroplasty. Among them are the use of donor cadaver tissue and the use of porous expanded polytetrafluoroethylene (ePTFE) vascular grafts. Cadaver tissue is used reluctantly due to the possibility of transmission of viral disease. The use of ePTFE vascular grafts gained popularity in the early 1990's after a publication ("GORE-TEX Interpositional Arthroplasty for Trapeziometacarpal Arthritis," Greenberg, J. and Mosher, J., Abstract, American Society for Surgery of the Hand, Toronto, 1990) highlighted excellent early results with the use of a rolled up GORE-TEX Vascular Graft (W. L. Gore and Associates, Inc., Flagstaff, Ariz.). Long-term data, however, indicated that rolled ePTFE vascular grafts were not suitable for this application and were susceptible to abrasion and particulation similar to the silicone implants ("X-Ray Changes After GORE-TEX Interpositional Arthroplasty: Evidence for Particulate Synovitis," Greenberg et al, Abstract, American Academy of Orthopedic Surgeons, 1990). Most patients were asymptomatic even 5 years after surgery and were subjectively very happy with their outcome. A few patients, however, never had relief of preoperative symptoms of pain and swelling, even three months to a year after surgery. In several cases, the ePTFE anchovies were removed and not replaced for fear of a lingering foreign body reaction. An interesting finding was that these patients continued on to a successful outcome with good function and little or no pain. It is hypothesized that during the period in which the anchovy was in place, scar tissue invaded the region providing a scaffold for structural support that was sufficient to allow removal of the anchovy without collapse. It was observed that perhaps the anchovy only served a temporary function, and that beyond three months some other natural mechanism allowed stability and function of the joint.
None of the described prosthetic interposition arthroplasty and CMC joint reconstruction devices have met with an acceptable degree of success. Problems are mostly associated with long-term break-down, loosening, or dislocation. For these reasons tendon interposition with or without suspensionplasty has remained the gold standard even despite the inherent problems associated with tissue graft harvesting and protracted operating room time.
The present invention relates to a resorbable interposition arthroplasty implant that provides improved performance in comparison to prior devices. Various other implantable orthopedic devices made from resorbable materials have been described. These consist primarily of devices such as plates, pins and screws for bone repair and various devices for the repair and replacement of tendons and ligaments. These devices, particularly those intended for the repair and replacement of tendons and ligaments, are designed to hold the adjacent ends of the adjacent bones of a particular joint in appropriate relationship while accommodating tensile loads, that is, they prevent further separation of the adjacent bone ends during use of the joint. For example, U.S. Pat. Nos. 5,514,181 and 5,595,621 describe elongated bioabsorbable ligaments and tendons in the form of a multilayered spiral roll of a three layer laminate of a foraminous layer, a film layer and a sponge layer. The described devices are intended to provide articles of high tensile strength along their longitudinal axes about which the spiral roll has been formed. The film layer serves to block cellular migration in radial directions inside the prosthesis.
An improved interposition arthroplasty material should provide enough mechanical integrity to allow effective maintenance of the space between the adjacent ends of adjacent bones, preventing impingement of those adjacent bone ends while enhancing the invasion of host scar tissue into the space thereby creating stability. As host scar tissue proliferates, the material would slowly resorb, eventually transferring load-bearing function entirely to the tissue. The material would be simple to use and eliminate the need to harvest autologous tissue while allowing an expedited surgical procedure and avoiding harvest site morbidity and long-term complications due to prosthetic breakdown.